Bump-attached wiring circuit board and method for manufacturing same

ABSTRACT

An object of the present invention is to manufacture a bump-attached wiring circuit board with which stable bump connections are possible, and there is no need for bothersome operations such as plating pretreatments. A bump formation etching mask  7  is formed on the bump formation side  3   a  of a metal foil  3  having a thickness (t 1 +t 2 ) equal to the sum of the thickness t 1  of a wiring circuit  1  and the height t 2  of the bumps  2  to be formed on a wiring circuit  1,  the bumps  2  are formed by half-etching the metal foil  3  from the bump formation etching mask  7  side down to a depth corresponding to a predetermined bump height t 2,  and a metal thin film layer  10  composed of a different metal from the metal foil  3  is formed on the bump formation side of the metal foil  3,  thereby providing a bump-attached wiring circuit board with which stable bump connections are possible, and there is no need for bothersome operations such as plating pretreatments.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a bump-attached wiring circuitboard having bumps of a uniform height, and to a method formanufacturing this board.

[0003] 2 Description of the Related Art

[0004] It is common practice to make connections with microscopic bumps(such as those with a diameter of 50 μm and a height of 30 μm) whenconnecting a wiring circuit board and electronic elements such assemiconductor elements or liquid crystal display elements, or whenconnecting layers in a multilayer wiring board.

[0005]FIGS. 3A to 3E illustrate a typical method for forming bumps ofthis size.

[0006] First, as shown in FIG. 3A, a two-layer flexible board 33 isprepared by affixing a copper foil 32 to a polyimide film 31, and thecopper foil 32 is patterned by photolithography to form a wiring circuit34 (FIG. 3B).

[0007] Next, a cover coat layer 35 is formed by a conventional method onthe wiring circuit 34 (FIG. 3C). For instance, a polyamic acid layer maybe formed on the wiring circuit 34 and patterned by photolithography,and a cover coat layer 35 formed by imidation. Alternatively, a resistink may be applied by printing.

[0008] Next, bump holes 36 are formed by irradiation with laser light inthe region of the polyimide film 31 corresponding to the wiring circuit34 (FIG. 3D), and then the cover coat layer 35 is covered with aprotective film (not shown) as needed, after which microscopic bumps areformed by growing metal bumps 37 over the wiring circuit 34 exposed atthe bottom of the bump holes 36 (FIG. 3E).

[0009] However, when the bump holes 36 are made by irradiation withlaser light, there is variance in their open surface area due tovariance in the smear amount clinging to the bottom of the bump holes36, and this results in the problem of considerable variance occurringin the height of the metal bumps 37. This makes it difficult to achievestable bump connection. It is particularly difficult to connectsemiconductor elements all at once to a wiring circuit by ultrasonicconnection. A plating pretreatment is also essential in order to improvethe adhesive strength between the wiring circuit 34 and the metal bumps37 formed on it.

SUMMARY OF THE INVENTION

[0010] The present invention attempts to solve the above-mentionedproblems encountered with prior art, and it is an object thereof toprovide a method for manufacturing a bump-attached wiring circuit boardwith which stable bump connection is possible, and there is no need forbothersome operations such as plating pretreatment.

[0011] The inventors arrived at the present invention upon discoveringthat bumps of a uniform height can be produced, without performingbothersome operations such as plating pretreatment, by half-etching ametal foil, whose thickness is equal to the sum of the thickness of thewiring circuit layer and a thickness corresponding to the metal bumpheight, down to a depth corresponding to the metal bump height, and thatif a metal thin film layer composed of a different metal from the metalfoil is formed on the bump formation side of the metal foil, thenadhesion will be improved between the bump formation side of the metalfoil and the insulating layer above, the chemical resistance of thewiring circuit board will be improved, separation between the metal foilon the bump side and the insulating layer above will be prevented, andstable bump connection can be achieved.

[0012] Specifically, the present invention is a bump-attached wiringcircuit board in which a cover coat layer is formed on one side of awiring circuit, an insulating layer is formed on the other side, andbumps that are electrically connected to the wiring circuit are formedprotruding from the insulating layer, wherein the wiring circuit and thebumps are integrally formed from a single metal foil, and a metal thinfilm layer composed of a different metal from said metal foil isprovided between the insulating layer and the side of the wiring circuiton which the bumps are formed.

[0013] Here, when the insulating layer is a polyimide film produced bythe imidation of a polyimide precursor layer, it is preferable if themetal thin film layer exhibits higher adhesive force with respect to thepolyimide precursor layer than to the metal foil. Favorable examples ofcombinations of the metal foil and metal thin film here include a metalfoil that is copper foil, combined with a metal thin film of nickel,zinc, tin, or a nickel-cobalt alloy. In this bump-attached wiringcircuit board, it is preferable for the cover coat layer to have aconnection opening for allowing access to the wiring circuit from thecover coat side.

[0014] The present invention is also a method for manufacturing abump-attached wiring circuit board in which bumps are formed on a wiringcircuit, comprising the steps of:

[0015] (a) laminating a protective film over the bump formation side ofa metal foil having a thickness equal to the sum of the thickness of thewiring circuit and the height of the bumps to be formed on the wiringcircuit, and forming a wiring circuit formation etching mask on thewiring circuit formation side of the metal foil;

[0016] (b) forming a wiring circuit in a predetermined thickness byhalf-etching the metal foil from the side with the wiring circuitformation etching mask;

[0017] (c) removing the wiring circuit formation etching mask, and thenproviding a cover coat layer to the wiring circuit;

[0018] (d) removing the protective film provided to the bump formationside of the metal foil, and then forming a bump formation etching maskon this bump formation side;

[0019] (e) forming bumps of a predetermined height by half-etching themetal foil from the bump formation etching mask side;

[0020] (f) removing the bump formation etching mask, and then forming ametal thin film layer composed of a different metal from that of themetal foil;

[0021] (g) forming a polyimide precursor layer over the metal thin filmlayer so as to bury the bumps; and

[0022] (h) etching back the polyimide precursor layer and forming aninsulating layer in a predetermined thickness by imidation.

[0023] With this manufacturing method, the wiring circuit is formedbefore the bumps are formed.

[0024] Further, the present invention is a method for manufacturing abump-attached wiring circuit board in which bumps are formed on a wiringcircuit, comprising the steps of:

[0025] (aa) laminating a protective film over the wiring circuitformation side of a metal foil having a thickness equal to the sum ofthe thickness of the wiring circuit and the height of the bumps to beformed on the wiring circuit, and forming a bump formation etching maskon the bump formation side of the metal foil;

[0026] (bb) forming bumps of a predetermined height by half-etching themetal foil from the side with the bump formation etching mask;

[0027] (cc) removing the bump formation etching mask, and then forming ametal thin film layer composed of a different metal from that of themetal foil;

[0028] (dd) forming a polyimide precursor layer over the metal thin filmlayer so as to bury the bumps;

[0029] (ee) etching the polyimide precursor layer and forming aninsulating layer in a predetermined thickness by imidation;

[0030] (ff) removing the protective film provided to the wiring circuitformation side of the metal foil, and then forming a wiring circuitformation etching mask on this wiring circuit formation side;

[0031] (gg) forming a wiring circuit in a predetermined thickness byhalf-etching the metal foil from the wiring circuit formation etchingmask side; and

[0032] (hh) removing the wiring circuit formation etching mask, and thenproviding a cover coat layer to the wiring circuit.

[0033] With this manufacturing method, the bumps are formed before thewiring circuit is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIGS. 1A to 1H are diagrams illustrating the steps in the methodof the present invention for manufacturing a bump-attached wiringcircuit board;

[0035]FIGS. 2A to 2I are diagrams illustrating the steps in the methodof the present invention for manufacturing a bump-attached wiringcircuit board; and

[0036]FIGS. 3A to 3E are diagrams illustrating the steps in aconventional method for manufacturing a bump-attached wiring circuitboard.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The various steps in the manufacture of the bump-attached wiringcircuit board of the present invention will now be described in detailthrough reference to the drawings.

[0038] First, a method for manufacturing a bump-attached wiring circuitboard in which bumps are formed on a wiring circuit, and in which thewiring circuit is formed before the bumps are formed (steps (a) to (h)),will be described step by step through reference to FIGS. 1A to 1H.

[0039] Step (a)

[0040] First, a protective film 4 is laminated on the bump formationside 3 a of a metal foil 3 having a thickness equal to the sum of thethickness t1 of a wiring circuit 1 (see dotted line in figure) and theheight t2 of the bumps 2 (see dotted line in figure) to be formed on thewiring circuit 1, and a wiring circuit etching mask 5 is formed on thewiring circuit formation side 3 b of the metal foil 3 (FIG. 1A).

[0041] The optimal values are selected for the thickness t1 of thewiring circuit and the height t2 of the bumps 2 according to theintended use of the wiring circuit board. For example, if the wiringcircuit board is to be used as a mounting board for semiconductorelements, then the thickness t1 of the wiring circuit can be set at 20μm, the height t2 of the bumps 2 at 30 μm, and the diameter of the bumps2 at 50 μm.

[0042] Any material used in the conductor layer of a wiring circuitboard can be used as the metal foil 3, but the use of a copper foil ispreferred.

[0043] The wiring circuit etching mask 5 can be formed by the screenprinting of a resist ink on the wiring circuit formation side 3 b of themetal foil 3. Alternatively, a photosensitive resin layer or a dry filmcan be provided and patterned by exposure and developing according toconventional methods.

[0044] Step (b)

[0045] Next, the metal foil 3 is half-etched from the wiring circuitetching mask 5 side to form the wiring circuit 1 in the conventionalthickness t1 (FIG. 1B).

[0046] The half-etching conditions (such as temperature and etchingliquid composition) can be suitably selected according to the materialof the metal foil 3, the thickness to be etched, and so forth.

[0047] Step (c)

[0048] The wiring circuit etching mask 5 is then removed by aconventional method, after which the cover coat layer 6 is provided tothe wiring circuit 1 (FIG. 1C).

[0049] The cover coat layer 6 can be formed by the screen printing of acoating material for the cover coat layer. Alternatively, aphotosensitive resin layer or a dry film can be provided and patternedby exposure and developing according to conventional methods. Also, alayer composed of a polyimide precursor such as polyamic acid can beprovided, patterned, and imidated by conventional methods to form thecover coat layer 6.

[0050] In providing the cover coat layer 6, it is preferable to providea connection opening 11 that will allow access to the wiring circuit 1from the cover coat layer 6 side.

[0051] Step (d)

[0052] The protective film 4 provided to the bump formation side 3 a ofthe metal foil 3 is removed by a conventional method, after which a bumpformation etching mask 7 is formed on the bump formation side 3 a (FIG.1D).

[0053] The bump formation etching mask 7 can be formed by the screenprinting of a resist ink on the bump formation side 3 a. Alternatively,a photosensitive resin layer or a dry film can be provided and patternedby exposure and developing according to conventional methods.

[0054] Step (e)

[0055] Bumps 2 of a predetermined height t2 are formed by half-etchingthe metal foil 3 from the bump formation etching mask 7 side (FIG. 1E).

[0056] The half-etching conditions (such as temperature and etchingliquid composition) can be suitably selected according to the materialof the metal foil 3, the thickness to be etched, and so forth.

[0057] Prior to this half-etching, the cover coat layer 6 may be coveredwith a protective film (not shown).

[0058] Step (f)

[0059] The bump formation etching mask 7 is removed by a conventionalmethod, after which a metal thin film layer 10 composed of a differentmetal from the metal foil 3 is formed (FIG. 1F).

[0060] It is preferable for the metal thin film layer 10 to be formedfrom a metal material that exhibits high adhesive force with respect toa polyimide precursor layer 8 (discussed below). This will afford betteradhesion between the polyimide precursor layer 8 and the metal foil 3,and therefore in subsequent chemical treatment (such as the etch-back ofthe polyimide precursor layer 8 in step (g)), separation can beprevented between the metal foil 3 and the polyimide precursor layer 8or an insulating layer 9 (see step (h)) produced by the imidation ofthis polyimide precursor layer 8.

[0061] Favorable examples of this metal thin film layer 10 when themetal foil 3 is an ordinary copper foil include metal thin films ofnickel, zinc, tin, and a nickel-cobalt alloy. These thin films can beformed by electroless plating, electrolytic plating, vacuum vapordeposition, or another such method.

[0062] If the metal thin film layer 10 is too thin, adhesion cannot besufficiently improved between the insulating layer 9 and the wiringcircuit 1, but if it is too thick, the obtained effect will notcorrespond to the increased thickness, so a preferable range is 0.01 to4 μm. In particular, when the metal thin film layer 10 is a thin film ofzinc or tin, the preferred thickness of this layer is 0.1 to 0.5 μm;when the metal thin film layer 10 is a thin film of a nickel-cobaltalloy, the preferred thickness of this layer is 0.1 to 4 μm; and when itis a thin film of nickel, the preferred thickness of this layer is 0.01to 1 μm.

[0063] In the removal of the bump formation etching mask 7, if the covercoat layer 6 is covered with a protective film, the protective film maybe removed at the same time.

[0064] Step (g)

[0065] The polyimide precursor layer 8 is formed over the metal thinfilm layer 10 so as to bury the bumps (FIG. 1G).

[0066] The polyimide precursor layer 8 can be formed by a conventionalfilm formation process from polyamic acid or the like. The imidationconditions can also be determined according to the type of polyimideprecursor and so forth.

[0067] Step (h)

[0068] The polyimide precursor layer 8 is etched back and imidated toform the insulating layer 9 in a predetermined thickness t3. This yieldsthe bump-attached wiring circuit board shown in FIG. 1H.

[0069] Next, a method for manufacturing a bump-attached wiring circuitboard in which bumps are formed on a wiring circuit, and in which thebumps are formed before the wiring circuit is formed (steps (aa) to(hh)), will be described step by step through reference to FIGS. 2A to2I. The structural elements in FIGS. 2A to 2I correspond to thestructural elements numbered the same in FIGS. 1A to 1H.

[0070] Step (aa)

[0071] First, a protective film 4 is laminated on the wiring circuitformation side 3 b of a metal foil 3 having a thickness equal to the sumof the thickness t1 of a wiring circuit 1 (see dotted line in figure)and the height t2 of the bumps 2 (see dotted line in figure) to beformed on the wiring circuit 1, and a bump formation etching mask 7 isformed on the bump formation side 3 a of the metal foil 3 (FIG. 2A).

[0072] Step (bb)

[0073] The metal foil 3 is half-etched from the bump formation etchingmask 7 side to form the bumps 2 of a predetermined height t2 (FIG. 2B).

[0074] Step (cc)

[0075] The bump formation etching mask 7 is removed by a conventionalmethod, after which a metal thin film layer 10 composed of a differentmetal from the metal foil 3 is formed (FIG. 2C).

[0076] Step (dd)

[0077] The polyimide precursor layer 8 is formed over the metal thinfilm layer 10 so as to bury the bumps 2 (FIG. 2D).

[0078] Step (ee)

[0079] The polyimide precursor layer 8 is etched back and imidated toform the insulating layer 9 in a predetermined thickness t3 (FIG. 2E).

[0080] Step (ff)

[0081] The protective film 4 provided to the wiring circuit formationside 3 b of the metal foil 3 is removed by a predetermined method, afterwhich a wiring circuit etching mask 5 is formed on the wiring circuitformation side 3 b (FIG. 2F).

[0082] Step (gg)

[0083] The metal foil 3 is half-etched from the wiring circuit etchingmask 5 side to form the wiring circuit 1 in the predetermined thicknesst1 (FIG. 2G).

[0084] Prior to this half-etching, the bumps 2 may be covered with aprotective film (not shown).

[0085] Step (hh)

[0086] The wiring circuit etching mask 5 is removed by a predeterminedmethod (FIG. 2H), after which the cover coat layer 6 is provided to thewiring circuit 1. This yields the bump-attached wiring circuit boardshown in FIG. 2I. It is preferable here to provide a connection opening11 that will allow access to the wiring circuit 1 from the cover coatlayer 6 side.

[0087] In the removal of the wiring circuit etching mask 5, if the bump2 is covered with a protective film, the protective film may be removedat the same time.

[0088] As shown in FIG. 1H and FIG. 2I, the bump-attached wiring circuitboard obtained by the above manufacturing method of the presentinvention is such that the cover coat layer 6 is formed on one side ofthe wiring circuit 1, the insulating layer 9 is formed on the otherside, and the bumps 2, which are electrically connected to the wiringcircuit 1, are formed protruding from the insulating layer 9, whereinthe wiring circuit 1 and the bumps 2 are integrally formed from a singlemetal foil, and the metal thin film layer 10 composed of a differentmetal from said metal foil is provided between the insulating layer 9and the side of the wiring circuit 1 on which the bumps 2 are formed.When the insulating layer 9 is a polyimide film produced by theimidation of a polyimide precursor layer, this metal thin film layer 10is preferably formed from a material that exhibits higher adhesive forcewith respect to the polyimide precursor layer than to the metal foil.For example, when the metal foil is a copper foil, the metal thin filmlayer 10 is formed from a thin film of nickel, zinc, tin, or anickel-cobalt alloy. This affords better adhesion between the polyimideprecursor layer and the metal foil, and therefore, in a chemicaltreatment (such as the etch-back of the polyimide precursor layer),separation can be prevented between the metal foil and the polyimideprecursor layer or an insulating layer 9 produced by the imidation ofthis polyimide precursor layer.

[0089] Also, since the cover coat layer 6 of this bump-attached wiringcircuit board has a connection opening 11 that allows access to thewiring circuit 1 from the cover coat layer 6 side, the board can beaccessed from both sides, and this helps in raising the mounting densityof electronic elements.

[0090] The present invention provides a bump-attached wiring circuitboard with which the bump strength is stable, stable bump connectionsare possible, and there is no need for bothersome operations such asplating pretreatments. In particular, bump connections on an integratedcircuit can be stably produced all at once ultrasonically.

[0091] The entire disclosure of the specification, claims, summary anddrawings in Japanese Patent Application No. 2000-210482 filed on Jul.11, 2000 is hereby incorporated by reference.

What is claimed is:
 1. A method for manufacturing a bump-attached wiringcircuit board in which bumps are formed on a wiring circuit, comprisingthe steps of: (a) laminating a protective film over the bump formationside of a metal foil having a thickness equal to the sum of thethickness of the wiring circuit and the height of the bumps to be formedon the wiring circuit, and forming a wiring circuit formation etchingmask on the wiring circuit formation side of the metal foil; (b) forminga wiring circuit in a predetermined thickness by half-etching the metalfoil from the side with the wiring circuit formation etching mask; (c)removing the wiring circuit formation etching mask, and then providing acover coat layer to the wiring circuit; (d) removing the protective filmprovided to the bump formation side of the metal foil, and then forminga bump formation etching mask on this bump formation side; (e) formingbumps of a predetermined height by half-etching the metal foil from thebump formation etching mask side; (f) removing the bump formationetching mask, and then forming a metal thin film layer composed of adifferent metal from that of the metal foil; (g) forming a polyimideprecursor layer over the metal thin film layer so as to bury the bumps;and (h) etching back the polyimide precursor layer and forming aninsulating layer in a predetermined thickness by imidation.
 2. Themanufacturing method according to claim 1, wherein the metal thin filmlayer formed in step (f) exhibits higher adhesive force with respect tothe polyimide precursor layer than to the metal foil.
 3. Themanufacturing method according to claim 1, wherein the metal foil is acopper foil, and the metal thin film layer is a thin film of nickel,zinc, tin, or a nickel-cobalt alloy.
 4. The manufacturing methodaccording to claim 3, wherein the thickness of the metal thin film layeris 0.01 to 4 μm.
 5. The manufacturing method according to claim 3,wherein, when the metal thin film layer is a thin film of zinc or tin,the thickness of the metal thin film layer is 0.1 to 0.5 μm.
 6. Themanufacturing method according to claim 13, wherein, when the metal thinfilm layer is a thin film of a nickel-cobalt alloy, the thickness of themetal thin film layer is 0.1 to 4 μm.
 7. The manufacturing methodaccording to claim 13, wherein, when the metal thin film layer is a thinfilm of nickel, the thickness of the metal thin film layer is 0.01 to 1μm.
 8. A method for manufacturing a bump-attached wiring circuit boardin which bumps are formed on a wiring circuit, comprising the steps of:(aa) laminating a protective film over the wiring circuit formation sideof a metal foil having a thickness equal to the sum of the thickness ofthe wiring circuit and the height of the bumps to be formed on thewiring circuit, and forming a bump formation etching mask on the bumpformation side of the metal foil; (bb) forming bumps of a predeterminedheight by half-etching the metal foil from the side with the bumpformation etching mask; (cc) removing the bump formation etching mask,and then forming a metal thin film layer composed of a different metalfrom that of the metal foil; (dd) forming a polyimide precursor layerover the metal thin film layer so as to bury the bumps; (ee) etching thepolyimide precursor layer and forming an insulating layer in apredetermined thickness by imidation; (ff) removing the protective filmprovided to the wiring circuit formation side of the metal foil, andthen forming a wiring circuit formation etching mask on this wiringcircuit formation side; (gg) forming a wiring circuit in a predeterminedthickness by half-etching the metal foil from the wiring circuitformation etching mask side; and (hh) removing the wiring circuitformation etching mask, and then providing a cover coat layer to thewiring circuit.
 9. The manufacturing method according to claim 8,wherein the metal thin film layer formed in step (cc) exhibits higheradhesive force with respect to the polyimide precursor layer than to themetal foil.
 10. The manufacturing method according to claim 8, whereinthe metal foil is a copper foil, and the metal thin film layer is a thinfilm of nickel, zinc, tin, or a nickel-cobalt alloy.
 11. Themanufacturing method according to claim 10, wherein the thickness of themetal thin film layer is 0.01 to 4 μm.
 12. The manufacturing methodaccording to claim 10, wherein, when the metal thin film layer is a thinfilm of zinc or tin, the thickness of the metal thin film layer is 0.1to 0.5 μm.
 13. The manufacturing method according to claim 10, wherein,when the metal thin film layer is a thin film of a nickel-cobalt alloy,the thickness of the metal thin film layer is 0.1 to 4 μm.
 14. Themanufacturing method according to claim 10, wherein, when the metal thinfilm layer is a thin film of nickel, the thickness of the metal thinfilm layer is 0.01 to 1 μm.
 15. The manufacturing method according toclaim 2, wherein the metal foil is a copper foil, and the metal thinfilm layer is a thin film of nickel, zinc, tin, or a nickel-cobaltalloy.
 16. The manufacturing method according to claim 9, wherein themetal foil is a copper foil, and the metal thin film layer is a thinfilm of nickel, zinc, tin, or a nickel-cobalt alloy.